expo.io 的 BackgroundFetch 没有运行定义的任务

Question

我目前正在使用 expo sdk-version 32 为iOS开发一个应用程序。我必须从我的应用程序定期致电REST服务。为此，我尝试使用新的BackgroundFetch API。

这是我的代码：

const BACKGROUND_LOCATION_SENDING_TASK = "BACKGROUND_LOCATION_SENDING_TASK";
async function initBackgroundLocationSending() {
    console.log("initBackgroundLocationSending()");
    TaskManager.defineTask(BACKGROUND_LOCATION_SENDING_TASK, () => {
        // this console.log does never get called ... 
        console.log("BACKGROUND_LOCATION_SENDING_TASK");
        // i will implement real fetch logic here when i found out how to get this function called.
        return BackgroundFetch.Result.NewData;
    });
    console.log("is task registered ... ");
    let isRegistered = await TaskManager.isTaskRegisteredAsync(BACKGROUND_LOCATION_SENDING_TASK);
    console.log("isRegistered: ", isRegistered);
    if(isRegistered) {
        console.log("unregister task ...");
        await BackgroundFetch.unregisterTaskAsync(BACKGROUND_LOCATION_SENDING_TASK);
        console.log("Done");
    }
    console.log("is task registered ... ");
    isRegistered = await TaskManager.isTaskRegisteredAsync(BACKGROUND_LOCATION_SENDING_TASK);
    console.log("isRegistered: ", isRegistered);
    console.log("register task ...");
    await BackgroundFetch.registerTaskAsync(BACKGROUND_LOCATION_SENDING_TASK);
    console.log("OK");

    console.log("is task registered ... ");
    isRegistered = await TaskManager.isTaskRegisteredAsync(BACKGROUND_LOCATION_SENDING_TASK);
    console.log("isRegistered: ", isRegistered);
    console.log("set minimum interval ...");
    await BackgroundFetch.setMinimumIntervalAsync(60);
    console.log("OK");
    console.log("get status ... ");
    const status = await BackgroundFetch.getStatusAsync();
    console.log("status: ", status);
}

从 app.js 中调用函数的控制台输出：

: initBackgroundLocationSending()
: is task registered ...
: isRegistered:  true
: unregister task ...
: OK
: is task registered ...
: isRegistered:  false
: register task ...
: OK
: is task registered ...
: isRegistered:  true
: set minimum interval ...
: OK
: get status ...
: status:  3

来自Expo的背景文档，我了解状态：3 表示BackgroundFetch.Status.Available。

ios 我的 app.json 的部分：

...
"ios": {
  "supportsTablet": true,
  "bundleIdentifier": "xxx-yyy-zzz",
  "infoPlist": {
    "UIBackgroundModes": [
      "location",
      "fetch"
    ],
    "NSLocationWhenInUseUsageDescription": "... (replaced)",
    "NSLocationAlwaysAndWhenInUseUsageDescription": "... (replaced)",
    "NSLocationAlwaysUsageDescription": "... (replaced)"
  }
},
...

我的测试设备是带有iOS 12.1.3的iPhone 6s。

我缺少什么？为什么甚至几分钟后都没有运行任务？

btw：我使用Expo的背景位置而没有任何问题

Answer 1

我会尝试通过将任务定义移动到文档状态，因为您当前设置它的方式在函数范围内定义

1. 通过提供一个名称和应执行的函数来定义任务：这需要在全局范围中调用（例如在您的反应组件之外）

意味着这个

const BACKGROUND_LOCATION_SENDING_TASK = "BACKGROUND_LOCATION_SENDING_TASK";
async function initBackgroundLocationSending() {
    console.log("initBackgroundLocationSending()");
    TaskManager.defineTask(BACKGROUND_LOCATION_SENDING_TASK, () => {
        // this console.log does never get called ... 
        console.log("BACKGROUND_LOCATION_SENDING_TASK");
        // i will implement real fetch logic here when i found out how to get this function called.
        return BackgroundFetch.Result.NewData;
    });
    ....
}

应该更改为此

const BACKGROUND_LOCATION_SENDING_TASK = "BACKGROUND_LOCATION_SENDING_TASK";
 TaskManager.defineTask(BACKGROUND_LOCATION_SENDING_TASK, () => {
     // this console.log does never get called ... 
     console.log("BACKGROUND_LOCATION_SENDING_TASK");
     // i will implement real fetch logic here when i found out how to get this function called.
     return BackgroundFetch.Result.NewData;
 });

async function initBackgroundLocationSending() {
    console.log("initBackgroundLocationSending()");
    ...
}

处理任务注册的initBackgroundLocationSending的其余部分应在组件安装